1. Field of the Invention
This invention relates generally to production of hydrocarbons from subsurface formations and more particularly to in-hole seismic data acquisition to map advancing fluid fronts within a field or around a single wellbore.
2. Description of the Related Art
In order to relatively precisely map advancing fluid fronts within a field or around a single wellbore requires the use of deep reading measurements at spatial resolutions of less than five (5) meters but with the spatial extents of several hundred meters, depending upon the reservoir location, size and the number of wells in the field. Conventional three dimensional ("3D") seismic acquisition and repeated 3D seismic acquisitions (also referred to as the 4D seismic acquisition) and seismic data acquisition techniques known as vertical seismic profiling ("VSP"), 3D VSP and Reverse VSP or Reverse 3D VSP are often utilized to model the reservoirs and/or to determine the advancing fluid fronts in the producing formations. The conventional 3D and 4D surface seismic acquisitions are performed by deploying detectors at or near the surface and the survey area is usually substantially large. The conventional 3D and 4D surveys provide data with limited spatial resolution and no near real-time ability to utilize results because of the lengthy time span required to acquire and process the data, which can take several months. The subsurface VSP and 3D VSP also suffer from long data processing cycles and have limited spatial extent.
Water breakthrough can occur rapidly, especially after a new horizontal well is drilled. Reservoir engineers can take timely action if the fluid front information is available timely.
Another related problem is the expense of acquiring repeat 3D seismic data over a relatively small geographical area, such as between 10-20 Km.sup.2. The current seismic surveying vessels using surface towed cables are designed to acquire vast volumes of data over a large region. Ocean bottom cable surveys, wherein seismic sensor or detector cables are deployed on the sea bottom, provide an alternative surveying method but are more expensive than the towed streamer cable acquisition methods.
Co-pending U.S. Pat. application Ser. No. 08/948,150, now U.S. Pat. No. 6,065,538, assigned to the assignee of this application, provides yet another alternative, wherein seismic sensors are deployed in wells formed for such purposes as close to the producing zones. Such techniques also are relatively expensive as they require drilling of additional wells.
The present invention provides systems and methods for acquiring seismic data by deploying movable clusters of seismic detectors in wells to acquire data as needed. Such a system provides seismic data with relatively high spatial resolution and with small spatial extent. Because of the relatively small number of detectors, the data can be processed substantially in real-time and utilized to provide 4D maps of the advancing fluid fronts. Use of such systems in multiple wells in a common field provides maps of the advancing fluid fronts within that field.